This invention relates to transmission lines for optical waves.
Many types of optical fibers having solid cores of transparent material such as glass or plastics have been developed and are being used as transmission lines for modulated optical waves. Diameters of these optical fibers typically range from a few micrometers to one millimeter. The smaller diameter optical fibers, being quite flexible, are more common and permit many transmission lines to be encabled, thus providing for multiple and/or redundant transmission circuits.
Energy losses due to attenuation in the available fiber optic materials and loss of coherence of the light due to multiple reflections currently limit the useful length of a section of fiber optic transmission line to a kilometer or 2. If longer distances are to be covered, amplification repeaters must be used to raise the signal level before injecting the signal into another section of optical fiber transmission line.
The small dimensions of the optical fibers cause immense problems in coupling with input and output devices, greatly affecting the cost and complexity of the repeaters.
In order to minimize the number of repeaters for a given length transmission line, intensive development work is currently under way both in the area of solid optical fiber technology and in the area of the peripheral devices. The scope of this work includes the use of multi-layered solid fibers to improve coherence and improvements in glass technology which is now approaching the theoretical limits of transparence. Still, others are actively striving to produce plastics capable of equalling the performance of quartz.
While these approaches offer potential improvement in increasing the useful length of optical fiber transmission line sections, the problems and cost of providing amplifiers remain a limiting factor in the commercialization of optical transmission lines for modulated optical waves.